Bass leaves after amp warms up?

I set up just analog no digital but w/power conditioner.
Once again I found the sold,dynamic sound.
I said if this stays I will forgo TV,DVD even CD.
But just 20 minutes into listening
I could hear the kick drum less & less
And over about 10 seconds my sound was gone.
When the song was over I had entirely different presentation than previous.
I went back to song #1 & it was crap
In a word anemic sounding
I just heard this song and it was powerful,clear,driving with punch..You name it the sound was the way I like it.
Before I could sit back and enjoy,it was gone.
I'm not making this stuff up..

It's been a while since I used stock power chords but will give it a shot.

Atmasphere I tried your suggestion of turning off the amp when the sound changes and my first try was successful!
I only waited 10 minutes and returned but the bass was back in full bloom.
I don't know how long it will last but will explore this development till I discern a pattern.
Something must be overheating?

Fishing, I can feel your frustration, but IMO nothing can be done w/o measuring the SPL. Wait for your friend to measure and then we'll have a more definitive diagnosis. (Underpowered amp as many of us believe). OK, my last post.

Fishing716 -

A couple of suggestions.
What I have found with some mosfet amps is they go through cycles. On turn on, very transparent, then after a while they go gluggy. However if you wait another hour then the transparency returns.
The other suggestion would be to get the amplifer checked over - get the "bias" checked to make sure it is in spec. The bias will determine the operating temperature to some degree and too high a bias can result in "gluggy" sound.